The present invention relates to a process and apparatus for replacing cathodes in the cells of an electrolytic plant. In the electrolytic plant suitable for practice of the present invention, rectangular cells are positioned side by side in a plurality of rows perpendicular to the longitudinal axes of the cells. Each cell contains a group of cathodes suspended vertically at equal distance from one another and perpendicular to the longitudinal axes of the cells. According to the general concept of the invention, when the electrolytic deposit which forms on the cathodes as a result of electrolysis has reached a required thickness,
(a) a subgroup of cathodes is lifted from a cell, while ensuring that the orientation and the disposition of the cathodes in the lifted subgroup remains identical to that originally in the cell,
(b) the lifted subgroup is conveyed to a stripping installation in which the electrolytic deposit is stripped off the cathodes, said stripping installation having an entry for cathodes to be stripped and an exit for stripped cathodes,
(c) the lifted subgroup is set down at the entry of the stripping installation,
(d) a series of stripped cathodes, corresponding in number, orientation and disposition to the lifted subgroup, is lifted from the exit of the stripping installation,
(e) this lifted series is conveyed to a position above said cell, and
(f) the lifted series of stripped cathodes is set down in the position from which said subgroup was lifted.
In any such process for replacing cathodes only a subgroup of cathodes in a cell can be removed at one time, e.g., half of the cell charge, since the cell has to remain under current during the replacement of cathodes.
A similar process has long been used for the production of starting sheets for the electrorefining of copper. This known process is carried out as follows. When starting the replacement of the cathodes, a compact subgroup of successive (adjacent) cathodes, e.g., the front half of the cell charge, is lifted from the first cell of a row of cells. This lifted subgroup is conveyed to the stripping installation and is set down at the entry of the installation which then begins to strip the cathodes. A return is immediately made to the second cell of the same row where, once more, the front half of the cell charge is lifted and, once more, this subgroup is set down at the entry of the stripping installation. This procedure is repeated with the remaining cells of the row until the stripping installation starts to deliver stripped cathodes. At this time when half of a cell charge, e.g., from the sixth cell, is set down at the entry of the stripping installation, movement is immediately made to the exit of the stripping installation where half of a cell charge of stripped cathodes is lifted; this lifted subgroup is conveyed to the first cell where it is placed in such a way that it replaces the absent front half of the cell charge. The next forward movement is from the seventh cell to the entry of the stripping installation and the backward move immediately thereafter is from the exit of the stripping installation to the second cell. The whole row is dealt with in this way, whereafter the cathodes of the back half of the cells of the same row are replaced.
Two disadvantages of this known process are (1) the unfavorable current redistribution in the cells when the cathodes are being replaced and (2) the requirement of at least four to-and-fro movements between the cells and the stripping installation to replace two full cell charges. The latter disadvantage presents problems particularly when working with a fast operating automatic stripping installation.
In order to avoid the latter drawback it has already been proposed to simultaneously replace several compact subgroups of cathodes, e.g., two subgroups positioned side by side in adjacent cells. In these suggestions, however, use is made of either a sophisticated conveying system, as described in the U.S. Pat. No. 3,562,131, providing for each row of cells, an overhead crane, two carriages each equipped with a rack and a conveyer-belt to the stripping installation, or a sophisticated moving stripping installation, as described in the German patent application No. 2,424,383.
The aim of the present invention is to provide a process that avoids the above-mentioned disadvantages.